A historic heat wave is sweeping across the Southwest and California this week, threatening to shatter hundreds of temperature records and push some cities into territory typically reserved for late spring or early summer. This unprecedented March warmth comes on the heels of the warmest winter on record for most of the American West.

The extreme heat began building over the weekend and will intensify through the week. According to The Weather Channel, above-average temperatures are dominating the West for the foreseeable future, with readings running 20 to 30 degrees above normal for this time of year. On Monday (March 16), Redwood City set an all-time March record after hitting 90 degrees, and nearly 90 other cities could follow suit this week.

For the Desert Southwest, this is shaping up to be an exceptional event. Phoenix could see multiple days exceeding 100 degrees, temperatures normally not reached until early May. The city's earliest recorded 100-degree day was March 26, 1988, and this heat wave could beat that record by more than a week. Los Angeles, Reno, Albuquerque, and scores of other Western cities face the possibility of all-time March temperature records falling.

The Bay Area is experiencing something entirely new for this time of year. Heat advisories have been issued in the region for the first time ever during March. Cities as far north as San Jose and Redding could approach 90 degrees, while parts of the Los Angeles basin may hit 100 degrees. The lower deserts of southeastern California and southern Arizona could reach 110 degrees, which would be the earliest such extreme temperatures have ever been observed in those areas.

The record warmth extends well beyond California and Arizona. The Colorado Front Range, including Denver, will likely see temperatures climb into the 80s. Sacramento Valley could approach or exceed 90 degrees. Hundreds of daily records are expected to fall across the West before the heat spreads into the Deep South by the weekend.

Meteorologists say they haven't seen a March heat event like this one, citing the combination of intensity, duration, and geographic scope as truly extraordinary. The atmospheric setup involves a powerful ridge of high pressure, the strongest mid-tropospheric ridge ever observed in the southwestern United States during March.

The extreme warmth follows Winter 2025-2026, which was the warmest on record across the majority of the American West, including nearly all of the Colorado River Basin and southern California's major metro areas. That record-setting winter has left snowpack at near-record low levels in many areas, and the current heat wave threatens to accelerate snowmelt dramatically during what should be a prime accumulation period.